Reaming arrangements have been proposed in the art previously. Generally speaking, reamers provide particular use in enlarging pilot holes previously drilled. The reaming bit is pulled through a drilled pilot hole rather than pushed and accordingly, a substantial amount of friction is received by the reaming faces and particularly at the cutting bits or buttons thereof.
During a reaming procedure when employing conventional reamer bits such as those of a cylindrical geometry, the friction experienced by the reaming face is not regular or uniform at all positions thereover. As a natural consequence, irregular wear occurs on the reaming face with the possibility of having completely "bald" areas on the face, completely devoid of cutting inserts, while other areas are unaffected. A further difficulty with present arrangements is that the same generally wear out to the point of being useless far too quickly.
In addition to the above, the present design of reaming bits in which the individual members of the bit are cropped together, provide a large number of areas between the individual members within which debris may become trapped. The result is that the individual members of the bit jam and subsequently are dragged within the formation. Such conditions eventually destroy the individual members of the bit and eventually the entire bit.
In a related matter, the reaming faces, when the same become worn or the cutting bits dull, etc., require replacement which poses a fairly involved procedure in terms of time. Generally, the bearings of the reaming faces are associated with the interior of the faces themselves. This is inconvenient when exchange or replacement is required. Since the overall reaming arrangement may present no further utility for reasons outlined above, the bearing system associated therewith may be in perfect working order, but must be discarded with the spent arrangement. This clearly has negative ramifications in terms of cost and productivity and is an unnecessary waste.
One of the primary difficulties in this art is the fact that many of the cutter arrangements presently patented are not true rolling arrangements. Due to the lack of this feature, there is at least a portion of the area of the roller cutter which becomes useless and is scuffed and prematurely worn out. This additionally creates problems in terms of the enormous torque forces that are required to operate the tool among other disadvantages.
Typical of the existing prior art in this field is exemplified by U.S. Pat. No. 4,399,879, issued Aug. 23, 1983, to Liljekvist et al. The Liljekvist arrangement provides a boring head in which there is provided a plurality of roll cutters, each rotatably journaled over a bearing system. The rollers in this reference do not have a semi-circular profile or subscribe to a semi-spherical shape, but rather are substantially frustoconical in shape.
Going, in U.S. Pat. No. 4,241,799, issued Dec. 30, 1980, provides a protective cutter mounting for drill bits. In the reference, the cutter is composed of a plurality of cutter assemblies which subscribe to a frustoconical shape. There is no provision for a multiple cutter head assembly where the heads provide a plurality of spherical faces.
In U.S. Pat. No. 4,641,718, issued to Bengtsson, Feb. 10, 1987, the patentee discloses a rotary drill bit comprising a cutter bit having a plurality of cutters within the body. Similar to the above references, the Bengtsson arrangement cannot provide a true rolling rotary drill bit and accordingly, this reference does nothing to solve the problem currently experienced in the drilling and mining art with respect to undue premature wear and limited use out of the bits and related equipment.
Other references which are generally relevant to the art to which the present invention is related includes U.S. Pat. Nos. 5,145,016, 4,591,008, 4,244,433, 4,280,571 and 4,484,783.